Time elapse telephone switching system



Dec. 10, 1957 F. A. MoRRIs ETAI.

TIME ELAPSE TELEPHONE swITcHING SYSTEM Filed April 23, 1954 17 Sheets-Sheet 1 BY ROBERT B. TROUSDALE ATTORNEY Dec. 10, 1957 F. A. MORRIS ETAL TIME ELAPSE TELEPHONE SWITCHNG SYSTEM Filed April 25, 1954 17 Sheets-Sheet 2 INVENTORS. FRANK A. MORRIS ROBERT B. TROUSDALE ATTORNEY 17 Sheets-Sheet 3 De l0, 1957 F. A. MORRIS ETAL TIME ELAPSE TELEPHONE SWITCHING SYSTEM Filed April 25, 1954 TIME ELAPSE TELEPHONE SWITCHING SYSTEM l liixiixxxx m l f* P hm Il. 5 a mm z w] Il i V Il LlNEI LINE2 lFIG. 4

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Dec. 10, 1957 F. A. MORRIS ET AL 2,816,168

TIME ELAPSE TELEPHONE SWITCHING SYSTEM Filed April 25, 1954 1'7 Sheets-Sheet 8 ATTORNEY Dec. 10, 1957 F, A, MORRIS ET AL 2,816,168

TIME ELAPSE TELEPHONE SWITCHIG SYSTEM Filed April 23, 1954 17 Sheets-Sheet 9 N l0 Q' o' o' Z Z Z m' D: [I u l uJ Lu O D O E Z Z u- Ll- LL f a S a l l o,

...4 ,LE Ll.. O I l y T INVENTORS.

FRAN K A. MORRIS ROBERT B.TROU$DALE ATTORNEY Dec. 10, 1957 F. A. MoRRls ET AL 2,816,168

TIME ELAPSE TELEPHONE SWITCHING SYSTEM Filed April 25, 1954 17 SheeLs-Sheetl lO OPOmZZOU Dec. 10, 1957 F. A. MORRIS ET AL TIME ELAPSE TELEPHONE SWITCHING SYSTEM 17 Sheets-Sheet ll Filed April 23, 1954 mON\ IN VEN TORS.

FRANK A. MORR|S BY ROBERT B.TROUSDALE ATTORNEY Dec. l0, 1957 F. A. MORRIS ETAL 2,816,168

TIME ELAPSE TELEPHONE SWITCHING SYSTEM Filed April 25, 1954 17 Sheets-Sheet l2 oUT#\ A PULSE GEN. D -JI--II--II-II-II-'I-I--JI-IMI-A-JL-JLL-JI-JL-A- oUT#2 F l l 1 sEo.PU| sE GEN. G '-l J l I I oUT I H r'T-T r1 f-I T T-1 r-l F-I r-L f J I I I I K l I I COMMUTATOR I l I OUTPUT I L I M I I l 0 r ALLOTTER OUTPUT 1p Q nl llo nl no' I I l I l I I l MULTIPLEXER R V I/ I 1 I OUTPUT usT FINDER OPEN) (2ND FINDER OPEN) oUTPUT oF TUBE 5| T I l l INPUT u. I To TUBE 11 VOLTAGE ACROSS v J CONDENSER 72 oUT oF TUBE 73 W l l l OUTPUT oF TUBE e5 Y Lf Y Y oUTPT Z L I\ 0F TUB B9 H2 oUTPUT AA I I/ II II 0F TUBE 95 sUPPBEssoR Be -1 n GRID TUBE 5I INVENTORS FRANK A. MoRR'ls FIG. II ROBERT B TRoUsDALE ATTORNEY Dec. 10, 1957 F.-A. MORRIS I-:T AI. 2,816,168

TIME ELAPSE TELEPHONE SWITCHIG SYSTEM Filed April 2:5, 1954 17 sheets-sheet 13 I 2 3 4 5 6 7 8 9 O f -fI I I I I I I I I I I I /I\ I I I I I I I I I4 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I i i I m l Y I I l I l MULTIPLEXER I I I I I I I A4 Y I I I I I I I I I I I I I I I Y I I I I I 'I' `I I I I /I\ I I I IFIG- l2 I I l I I l I I I l l l I I I I l I I I I I I I I I I I I I I I I I I I I /I\ I I I I I I I I I I I I I I I Ir I I I I OUTPUT FROM I A I AI I ,L I I I MuLrIPLExI-:R B

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ATTORNEY De 10, 1957 F. A. MORRIS ETAL TIME ELAPSE TELEPHONE swITcHING SYSTEM 17 Sheets-Sheet 14 Filed April 23, 1954 LINES l l l wml INVENTORS. FRANK A. MORRIS BY ROBERT B.TROUSDALE J 2. @www W wuz...

ATTORNEY Dec. 10, 1957. F. A. MORRIS ETAL 2,816,168

TIME ELAPSE TELEPHONE SWITCHING SYSTEM Filed April 23, 1954 17 SheetS-Sheeb l5 DISTRIBUTOR MULTIPLEXER INVENTORS. FRANK A. MORRIS ROBERT B.TROUSDALE ATTORNEY Dec. 10, 1957 F. A. MORRIS ETAL 2,816,168

TIME ELAPSE TELEPHONE SWITCHING SYSTEM Filed April 23, 1954 17 Sheets-Sheet 16 T0 IN GATE AMPLIFIER SOURCE OF COMMUTATING VOLTAGE FROM DISTRIBUTOR IBS FIG. I8

JNVENToRs. FRANK A. MoRms BY ROBERT a.TRousDA| ATTO RNEY 10,1957; 1' v F. A. MORRIS Erm.

TIME ELAPSE TELEPHONE swITcHING SYSTEM AFiled Aprile; 1954 17 Shegts-Sheet 1'7 of v Y mmazr...) 1

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INVENTORS. FRANK ILMORRIS BY ROBERT B TROUSDALE di 92.5228 v, Y m3242256 Fzuneum n mz3 rsu o sunaum aun ATTORNEY 2,3 l ti l @ii Patented Dec. Mi, i955? ice 2,8%,1623 TIME ELA-.PSE EELEPHQNE SWiCHiNG SYS'EERI Frank A.. Morris, Rochester, and Robert E. Tronsdale, Webster, N. Y., assignors, by mesne assignments, to General Dynamics Corporation, a corporation et' Delaware Appiication April 23, 1954, Serial No. 42S,ii94

14- Clainis. (Cl. 179-15) This invention relates to telephone systems and more particularly to electronic switching means for use in automatic telephone systems.

It is an object of this invention to provide a new and improved telephone system in which some or substantially all mechanical relays or step-by-step switches are eliminated at a reasonable cost and which is eiiicient and positive in operation, inexpensive to maintain, and relatively simple to install and maintain.

It is another object of this invention to provide a new and improved inding means of an electronic type operating on pulse multiplex principles and having provision for allotting each finder to a calling line, for rendering each seized finder circuit inoperative to calls on any except that particular calling line, and for preventing loss of a seized nder during dialing or because of the accidental or temporary loss of signal pulses, as for example, hook switch tumbling, slow dialing, etc.

The automatic telephone system described and claimed herein utilizes a finder the operation of which is based upon a principle which may be termed, for convenience, the Time elapse principle and utilizes pulse transmission, the pulses representing the various calling lines being multiplexed or intermixed.

In carrying out the principles of this invention, pulse transmission is based upon the utilization of pulses to take spaced samples of the desired signal or intelligence to be conveyed. The effect is the same as plotting a smooth continuous curve from a few points by assuming that a.y If more de-Y rate approximately two and one-half `times the highesty desiredy frequency. lt should be noted that theA width of the sample is of very little importance to the reconstruction providing itis no more than one half as wide as a cycle of the highest desired frequency. The pulse carrier bandwidth is determined by the'width of the pulse itself, however, for the narrower the pulse, the wider the band. Modulation has no eect upon the bandwidth. A single pulse sample contains information only as to the voltage of the sampled signal at that instant. This information can be impressed in a number of ways such as pulse height, Width, or displacement.

Several audio signals may beV transmitted over a single channel by merely staggering the positions ,of pulse samples. The several signals may be separated at the receiving terminal. Bandwidth utilization is comparable to that of conventional frequency displacement (carrier) systems but the overall economy is` greater due to the relatively simple equipment needed to combine and sepgrate the several signals. Multiplexequipment `is Aalsocompact and either of these factors is far more important in a telephone exchange than in toll transmission networks where pulse methods are already applied.

In accordance with the preferred embodiment of this invention, there is provided a gate which may resemble closely an amplifier, employing one or more electron discharge devices, and which may be called for convenience, an irl-gate. An allotter is provided 'for successively enabling or preparing for conduction upon receipt of a signal pulse the various finder in-gates for a predetermined period, as one frame of signal pulses, a frame comprising a time period permitting a pulse corresponding to each line in the group to be multiplexed. The circuits are arranged so that only one in-gate is enabled by the operation of the allotter at any one time whereby each finder is successively available for `the duration of one frame. c

Each signal pulse corresponding to a seizing line is passed through the finder to succeeding circuits. In addition each passing signal pulse is utilized to close the ingate immediately after the passage of the pulse to prevent the allotted yiinder from being affected by the allotter during the remainder of the call, to transmit outgoing lockout pulses to all other linders at the time positions corresponding to the calling line throughout the duration of the call, and to start a frame timer for re-enabling the in-gate amplier at the expected times of the succeeding pulses corresponding to the calling line. y

It should be remembered that the elapsed time between eachsignal pulse corresponding to a given `subscribers line, regardless of its time position within the' frame, is the same and equal to the duration of a frame. The frame timing means is, therefore, arranged to measure off an identical period starting immediately after each desired signal pulse is received and ending just before the next signal pulse representing the same line appears at the in-gate. The frame timer re-opens the gatel just in time to pass the next correct signal pulse where-` upon the whole process is repeated successively until no more signal pulses are received.

The finder is thereby controlled to accept only signal pulses having the same time positions as the signal pulse which caused the finder to seize the calling line and other findersare rendered incapable of accepting pulses corresponding to the time position of a calling line because of the lockout pulses which paralyze their in-gates at that time position.

It is desired to prevent loss of a nder because of ternporary or accidental loss of signal pulses, due to dialing, etc. For this purpose, there is contemplated provision of an auxiliary gate for the purpose of introducing a train of dummy or auxiliary pulses occurring at the same rate as the signal or multiplexer pulses and which have identical time positions as, the signal pulses. These auxiliary pulses are utilized to assist in the switching and timing functions referred to above. To prevent loss of a finder by accidental or temporary loss of pulses for any reason, delay means is associated with the auxiliary gate amplifier as, for example, by providing a resistancecapacity network charged by signal pulses, the time constant being suiciently long so that momentary interruptions do not stop the flow of auxiliary or control pulses into the finder. This feature of vthe herein described and illustrated system is not'our invention but is the sole invention of Frank A. Morris, assigned to the same assignee as our invention and described, illustrated, and claimed in copending application Serial No. 425,093, led April 23, 1954.

The system' to be described is based upon decimal principles. Lines are preferably grouped by tens, and each group of ten lines is provided with a multiplexing circuit, the multiplexing circuit being arranged to sample each line and to combine. pulses representing the samples into a single train of pulses. There is provided, for overall control purposes, a suitable source of Y pulses of a suitable frequency, as for example, 100- kilocycles. The pulses obtained from this source are commutated and employed for sampling each line successively inthe multiplexer. The outputof the multiplexer, therefore, comprises a succession of frames of pulses, each frame including ten equally spaced pulses correspondingy successively to the ten lines of the calling group. Thus, each frame is divided into ten periods, corresponding periods in each frame representingthesame l in'e. The pulses may be modulated by 'an audio or signalvoltage representing the sounds or other intelligence to be cornmunicated or by dial impulses.r

The activation ofa line by a subscriber, als by lifting his receiver, causes pulses to appear at the finders at regular intervals, the exact time positions of the pulses being dependent upon the particular line activated. Speech and dialing signals are conveyed by these pulses by affirm of amplitude modulation, then multiplexed pulses' Vbeing provided at a relatively highrepetitiori rate as, for ex'- ample, ten kilocycles per second.

Common equipmentl may be shared byineorporatinga plurality of line finders, as four, for example'to'constitute a group, within whichl each Hnderis connected to all: subscriberslines included in the particular multiplexed group associated with this group ofiiiiders. A; lind'er to pass mul- The primary purpose ofeach line tiplexed pulses to succeeding equipment. Secondary p urf.

poses include the generation' of lockout pulses to be transmitted or impressed upon other nders in the ygroup to cause suchV other indersto ignore the signalsrepresentf ing the calling linev which has been sized; as for example,Y

by sending suitable pulses to the `other finders to cut ol or close their in-gates, i. e., prevent allotter pulses from opening the gates included in .the other l'indeisfor the duration of the lockout pulses. If thelockoutpul'ses are timed to straddlethe time locations of the found or seized line pulses, the lockout pulses do notaffect-ad'- jacent multiplexed pulses `corresponding to other lines' in the calling group.

Other objects and advantages of our invention will become apparent as the following description proceeds, and the features ofnovelty which characterize our inverttion will be pointed out with particularity in theclairns annexed to and forming a part of this specification'. For a better understanding Aofour inventon, reference may be had to the accompanyng drawings in which:

Figs. 1 and 2 show in block diagram form different embodiments of our invention; H

Fig. 3 illustrates a suitable pulse generator for use in our system; f v

Fig. 4 illustrates a typical linecircuit and a suitable multiplexer circuit embodying the principles of the inventon;

Fig. 5y illustrates the basic features of .a suitable sequen tial generators for use in the telephone system disclosed herein; f l

Fig. 6 shows typical vcircuits for a channel pulse Acommutator for use with the foregoing components of a system; l,

` Figs. 7, 8 and 9 when taken together illustrate a finder embodying the principles of our invention;

Fig. l0 discloses a suitable connector for use in the' system described herein;

Fig. 10A discloses a suitable out-gate for use in our system;

Figs. 11, 12 and 13 illustrate typical conditions inthe system described herein; I i l,

` Fig. 14 is a chart illustrating the properi'elationship of Fig. 3 to 10A, inclusive, these ligures when laid next to each other as indicated, illustrating a one-way communcation system;

Fig. 15 shows in block form an arrangement utilizing the principles of our invention for providing two-way communication;

Fig. 16 shows a modification of Fig. 15;

Figs. 17, 18 and 19 show alternate forms of multiplexers,

Fig. 20 illustrates a timing circuit which may be employed in my system.

In Fig. 1 there are illustrated components of a system, shown in block form, for accomplishing the previously described functions. There is provided a suitable sequential pulse generator 140 for sequentially causing a multiplexing device 141 to sample successively the line circuits 142 assigned to that particular multiplexer. In the output of the multiplexer there appears a train of pulses, each pulse representing a calling line and having a time position within each frame or complete cycle representing a single sampling of each line in the calling group of lines including the calling line. The relationship of input and output pulses wth respect to multiplexer 141 are shown in Fig. 12A and Fig. 12B, respectively. The output from multiplexer 141 comprises, in a single frame, one or more successive pulses depending upon thel number of lines in off-hook or calling condition.

For each group of lines there is provided a plurality of finders. We have shown four linders, Finder No. 1 being indicated by the numeral 144.

Each nder is allotted successively for a single frame to Vtest for calling lines, i. e., is made responsive to multiplexer output pulses, by means of suitable signal or control quantities, such as suitable pulses from a suitable allotter 143. Assuming that the allotter has allotted finder 144, in-gate 14411 is made responsive to pulses received from multiplexer 141. Pulses passing through ingate 14411 are forwarded through succeeding equipment such as connector 145, and distributor 146 to the called line, as 147, for example.

Each finder of the type shown in Fig. 1 is provided with aA trigger circuit 148 and a timing circuit 149. Each signal pulse passing through in-gate 144a is utilized to block or cut-off in-gate 144:1 immediately after passage ofthe pulse and to trigger circuit 148 to start a timing cycle arranged to re-open or again enable in-gate 1440 at such a time as to pass the next pulse corresponding to thelseized callingA line. Each pulse is also utilized to block and maintain blocked the allotter gate 150.so that Fnder No. 1 cannot beallott'ed to another call, Pulses are also conducted to the other finders vin the finder group to prevent operation of the other finders in response to pulses representing the line seized by vFinder No. 1.

Thus, thereis provided a finder arranged to accept and pass only signal pulses having the same time position as the pulse which triggered it.

Means is provided for connecting an extended calling line to a called line including, a connector 145 land, distributor 146. Connector 145 may comprise means to translate the signal pulsesinto a step representationof the'signal. being communicated. The translator isfgenerally represented by numeral 151. I'n order toy choose the called line, dial impulse counting means 152 is utierators 140 and 155 may be a single source of pulses.

Connector accepts pulses having a time position corresponding to the calling line and forwards or re-transmits pulses in a new time position corresponding to the., The new time position is determined by line which control is determined by dialing 'at the call-y asientos ingstalion:` The new pulsev is released just as the distributoris incondition to pass pulses to the called line. The distributor may comprise a circuit similar to that used in the multiplexer 141.

There is illustrated in Fig. 2 a modification, shown and claimed in the above-identied copending application, utilizing auxiliary or dummy control pulses to avoid loss of connections by slow or faulty dialing, flashing, etc. With this arrangement, instead of employing signal pulses to trigger the timing circuit, the signal pulses are utilized to enable or prepare an auxiliary gate 156 for operation upon receipt of auxiliary or control pulses in synchronism with the multiplexed pulses. Separate pulse sources may be used but a single pulse generator 140 as indicated in Fig. 2 is preferable. The auxiliary gate is held open by a suitable slow release or holding circuit 157 such as a resistance-capacity network charged by signal pulses so that momentary or accidental interruptions do not release the nder.

In order to simplify an understanding of this invention, the ,disclosure has been limited to the essential features of the invention and functions which are not intimately connected with the subject matter claimed herein, such as dial tone, ringing, and busy tone, for example, have been omitted, such features being shown and described in detail in a copending application of Frank A. Morris and Robert B. Trousdale, Serial No. 134,974, filed December 24, 1949, and assigned to the same assignee as the present invention.

Pulse generator In Fig. 3 of the drawings there is illustrated a pulse generator which may be employed as a source of pulses. The generator shown in Fig. 3 comprises a suitable oscillator 1 and two output circuits 2 and 3 coupled to the load side of oscillator 1. Oscillator 1 is illustrated as being of the crystal controlled type, although the degree of stability inherent in this type of oscillator may not be necessary, and in such cases other forms of oscillators may be substituted. The arrangement and operation of oscillators of this nature is so well known that further description is not included in this specification. The circuit elements are preferably so chosen that the oscillator operates at a rate of one hundred kilocycles per second or thereabout.

The output circuits 2 and 3 are coupled to the output or plate circuit of the oscillator 1. For example, the plate or anode circuit of oscillator 1 may include a suitable coil or winding 4` and the inputs to output circuits 2 and 3 linayinclude coils 5 and 6, respectively, shunted by suitablevariable capacitors 7 and 8, respectively, to permit tuning of the output circuits 2 and 3 with respect to each other. The windings S and 6 are preferably loosely coupled to the coil 4 and the tuning means permits phase shift between the circuits 2 and 3 for a purpose to beI explained more fully hereinafter. Each of output circuits 2 and 3 is arranged to convert the sine wave output of oscillator 1 into relatively sharp pulses by including high-Q inductances 9 and 10 as the anode loads of heavily biased electron discharge devices 11 and 12, respectively, in'circuits 2 and 3, respectively. Shock excitation of circuits 2 yand 3 tends to produce high-frequency transient trains which are cut off at the first reversal by unilateral devices 13 and 14, respectively, which shunt inductances 9 and 10, respectively. Crystal diodes have been found to be suitable for this purpose.

Referring to Fig. 11 of the drawings, there is illustrated. at Athe output of the oscillator 1 and at B typical transient waves set up in-the output circuits, this iigure representing the output of circuit 3. By reason of the inclusion of crystal diode 14, the transient curve at Fig. ll-B is limited to onlyone loop as shown in solid lines, the suppressed portion of each of the transients being indicated jin Fig. 11B -by the dotted extensions of the..

curves.

The unsuppressed negative pulses are then amplified and inverted in suitable ampliiers 15 and 16, respectively, and delivered at low impedance by cathode followers 17,l

and 18, respectively. Referring again to Fig. l1, there are represented at C the relatively narrow spaced-apart, pulses of positive sense which appear across cathode're-' sistor 19. If the phase shift between circuits 2 and 3 is degrees, the similar relatively narrow spaced-apart` pulses of positive sense which appear across cathode re sistor 20 of cathode follower stage 18 are as represented at D of Fig. 11. y f

The output circuits 2 and 3 thus are utilized to produce two sets of relatively sharp pulses which maybe displaced with respect to times of occurrence by means of tunable secondary circuits.

One set of the foregoing pulses is used, in the present embodiment of our invention, to excite a sequential -pulse generator having `one stage for each line in the calling A group, two stages of which are shown in Fig. 5. For expulses for purposes hereinafter described, as for example to enable or maintain operation of each finder during the temporary or accidental absence of pulses, as during dialing by the calling party, and to perform timing functions.

Sequental pulse generator There is illustrated in Fig. 5 of the drawings a suitable sequential pulse generator for use in carrying out the principles of our invention. As described heretofore, one set of pulses from the pulse generator shown in Fig. 3 is employed to drive or excite the ring circuit `constituting the sequential pulse generator in the present embodiment of our invention. It is understood that there is actually employed one stage for each line in the calling group, the output of the last stage being connected to drive the tirst stage. For convenience, only two stages are shown in the drawing. Each stage comprises an Eccles-Jordan circuit including electron discharge devices, as of the pentode type, represented by the numer` als 30, 31 and 34, 35, respectively for the two stages shown. The output of each stage is coupled to a catliode follower including a suitable discharge device, as for example triodes 32 and 32a, respectively, in order to provide output at low impedance. The resulting square wave output pulses may be called gate pulses and are used for commutating the channel pulses and for gating the distributor as more fully described hereinafter.

Referring to each stage of the sequential pulse generator, the components are so disposed that the upper tubes of each stage constitute the off section, the anode of which is coupled by a suitable coupling capacitor, as-

Sfm, to the input side of the associated cathode follower stage. If it is assumed that the upper discharge device 30 of the irst stage is conducting, the upper devices of the other stages are non-conducting and remain non-conducting until something occurs to trigger the next upper discharge device 34. When a pulse appears over conductor 33 from the pusle generator, it is amplified by a suitable.

amplifier 36 and then applied to the cathodes and suppressor electrodes of each upper device. The appearance of a positive pulse on the cathode of device 30 cuts off the discharge device 30. thereby resulting is impressed upon the control electrode of the lower discharge device 31 in the first stage causing it to become conductive. At the same time, the higher anode voltage of device 30 is impressed upon the control electrode of the upper device 34 of the second stage The higher anode potential 

